The present invention deals with an optical data storage disk, at which, considered from a disk surface propagating in the direction of the disk thickness extent, at least two interfaces are provided, each of which being profiled according to stored information and whereby the profiled interface disposed innermost comprises a reflection layer, and the at least one further profiled interface comprises a partially reflecting/partially transmitting layer respectively for light of a given wavelength and under the same angle of incidence  less than 90xc2x0, whereby further the remaining disk material between the surface and the reflection layer substantially transmits the said light and whereby the reflection layer is made of a first metal alloy, the partially reflecting layer of a second metal alloy.
Such a data storage disk is known from the U.S. Pat. No. 5,640,382. Departing from the one disk surface and propagating in direction of the thickness extent of the disk, such disk comprises first a transparent substrate, then a partially reflecting layer on a first information-profiled interface, then a transmitting distance holder layer and finally a highly reflecting layer on a second information-profiled interface. The first mentioned transparent substrate may thereby be of a polymer material, as e.g. of polycarbonate, or of amorphous polyolefine. On the other hand it shall be possible too to use glass or a polymethylmetacrylate. It is known (see other publications) to construe such substrate of PMMA.
The distance holder layer further consists e.g. of a polymer. The highly reflecting layer, for laser light between 600 and 850 nm, is made of aluminum, gold, silver, copper or of one of their alloys. The wavelength band for laser light may, as known from other documents, reach down to 500 nm.
Preferably and according to the said US patent there is used for the partially reflecting layer preferably gold, due to its optical characteristics and especially its stability with respect to ambient influences. Nevertheless, there is recognised that gold is expensive. Therefore, there is further proposed to use gold alloyed with a less expensive metal, so as to reduce costs. Thereby, there is still used 10 at % gold and preferred up to 20 at % gold in the alloy for the partially reflecting layer so as to maintain stability with respect to ambient influences.
As gold alloying metal there is proposed silver or copper. The U.S. Pat. No. 5,640,382 shall be considered as integral part of the present description with respect to structure of an optical data storage from which the present invention departs.
For such optical data storage disks, e.g. realised as DVD9, Digital Versatile Disks, according to definition in DVD standard xe2x80x9cDVD Specifications for Read-Only Disksxe2x80x9d, Version 1.0 of August 1966, it is requested that at a given wavelength of laser light, especially at 650 nm, the laser light which exits, due to the reflections on one hand at the partially reflecting layer and on the other hand at the reflection layer, comprises respectively 18 to 30% of light applied to the disk. As DVD9 it is customarily understood a xe2x80x9csingle sided dual layer diskxe2x80x9d.
It is an object of the present invention to provide an optical data storage disk as mentioned above which
fulfils the specifications as mentioned above with respect to beam splitting,
is considerably less expensive with respect to its production,
features layers with a chemical resistance with respect to ambient influences, as e.g. with respect to corrosion, which fulfil requirements to a similar extent as do known data storage disks.
This object is resolved at the data storage disk mentioned by the facts that
the alloys of the at least two layers comprise one or more than one equal metal(s), whereby said one or said more than one metal(s) commonly represent a fraction of more than 50 at % of the respective alloy,
if said alloys comprise gold, this only to a fraction of at most 50 at % of the respective alloy.
By the fact that the alloy comprises one or more than one equal metal(s) with a fraction with respect to the respective alloy of more than 50 at %, it becomes possible to use, at least for this respective fraction of alloy, the same coating source arrangement. Thereby the basic is realised so as to significantly rationalise the manufacturing process for the said data disk. By the fact that further, if at all gold is used at the one and/or the other of the alloys, this is only done with a fraction of at most 50 at % of the alloy material, it is further reached that, also due to costs of the used alloy materials, the inventive disk is of lower costs with respect to manufacturing.
Although it is absolutely possible to select the said more than one equal metals which form a fraction of more than 50 at % of the respective alloy materials layer-specifically with different fractions, in a preferred embodiment it is proposed to select the said equal metals at the alloys with equal fractions and thereby preferably to select the fraction of the totality of the said equal metals at the alloy material to be equal.
Thereby, it becomes possible to operate a coating source arrangement for the said equal metals layer-unspecifically, thus equally when depositing both layers.
In a further preferred form of realisation it is proposed that the alloys are formed by equal metals, thereby preferably with the same alloying fractions. Thereby, it is evident that further elements as N, O, Ar may be present just in a trace concentrations. Therewith, the layers may further be deposited with the same coating source arrangement.
In a first especially preferred form of realisation of the inventive data storage disk the mentioned metals which respectively are present with a fraction of more than 50 at % at the respective alloy materials which further preferred make up the alloy are
AgxMayMbz or
CuxMayMbz,
with x greater than 50%, whereby x may vary layer-specifically within the indicated limit. Ma and Mb thereby indicate respectively a second and third metal.
Further and in an especially preferred form of realisation and especially with using AgxMayMbz, it is proposed to use palladium as the second metal Ma, thereby with y greater than z, this means with a fraction which is higher than that of an eventually provided third metal Mb. It is to be pointed out that all values indicated in the present description and in the claims for x, y, z shall be understood as at % of 100 at % layer material alloy.
It is further proposed that there is valid:
0 less than y less than 10 and
0 less than z less than 10,
which means that if the alloys mentioned above consist of the three metals mentioned, there results for Ag and respectively Cu:
x=100xe2x88x92yxe2x88x92z.
In a further preferred form of realisation without a third metal there is valid:
0 less than y less than 15 and
z≈0,
which leads to silver-palladium alloy layers and/or to Cu-palladium layers, thereby clearly preferring silver-palladium layers.
Thereby, it is further proposed that there is valid:
5 less than y less than 10 and
z≈0,
which is especially preferred for silver alloy layers with palladium, thereby preferably for layers which exclusively consist of the silver-palladium alloy.
Especially for such layers, namely of silver-palladium alloys, it is proposed to select:
y=8 and z≈0.
Although these values are also preferred for
Cux May Mbz,
especially also for copper-palladium alloys, it is most preferred to make use respectively of a silver-palladium alloy or of an alloy which comprises respectively silver and palladium to a fraction of more than 50 at %.
As the above mentioned second or third metal Ma, Mb respectively and especially as Ma, in this case instead of palladium indicated as preferred, one may also use gold with
y greater than z.
If for the said at least two layers the same alloy is used and thus the index of refraction of both alloys may be indicated by n and the absorption coefficient with k, there is preferably valid:
0 less than n/kxe2x89xa60.28, and thereby especially preferred
0 less than n/kxe2x89xa60.20.
This is valid for light with xcex=650 nm and the layer material in bulk form. Thereby the characteristics of the reflection layer substantially accords to the characteristics of the material in bulk form due to the thickness of that layer. Further there is valid for all metal alloys k greater than 2.
In a further preferred form of realisation of the inventive data storage disk the stability of the optical characteristics, especially of the layers, thus reflection, transmission and absorption, is better than xc2x12%, even better than xc2x11% when exposed to air during 24 h.
Further, the above mentioned object, with respect to specifications, low cost manufacturing and chemical resistance, is already resolved by the fact that irrespective of the realisation of the reflection layer, the partially reflecting layer consists of
Agx MayMbz,
or of
CuxMayMbz 
with x greater than 50%, whereby there stands:
Ma: for a second metal, besides of gold
Mb: for a third metal, preferably excluding gold.
Thereby it is possible to realise principally large cost savings even when construing deposition of the reflection layer e.g. of an aluminum alloy compared with depositing well-known alloys for the partially reflecting layer.
In a preferred embodiment the partially reflecting layer consists of AgxMayMbz, and there is applied as the second metal Ma palladium. There is thereby valid y greater than z.
Further, there is preferably valid at the partially reflecting layer:
0 less than y less than 10 and
0 less than z less than 10.
On the other hand there is valid in a further preferred embodiment and with respect to the partially reflecting layer:
0 less than y less than 15
z≈0, and thereby preferably
5 less than y less than 10, further with
z≈0.
In a today especially preferred partially reflecting layer, especially consisting of the AgPd alloy, there is valid:
y=8
z≈0.
Attention is especially drawn to the high ambient stability of the mentioned alloys and especially of the AgPd alloy, exploited as a material for the partially reflecting layer, as will be apparent from the following description.